1. Field of the Invention
This invention relates to a slide frame which is made of elastic plastic and has an entrance slit which is adapted to be expanded throughout the width of the transparency to be inserted.
2. Description of the Prior Art
Such slide frame is known from German Patent Publication No. 12 64 098, the applicant of which is the assignee of the present invention. In the use of the known slide frame, the film is inserted into the frame through the entrance slit. When the leading edge of the film has passed along the entire picture gate of the slide frame, it must be inserted into the slide frame also at that end thereof which is opposite to the entrance slit. This may give rise to difficulties if the film is cambered.
In most plastic slide frames the film-receiving pocket is closed at one end. This is apparent, e.g., from Austrian Patent Specification No. 231,195. It is known that a transparency is not perfectly planar, as a rule, because the film may be considerably cambered as a result of its development, particularly in film-suspending developing machines, or of a fast drying.
To ensure that the transparency in spite of its inevitable camber can be moved to a proper position for projection, i.e., into a film-receiving groove formed between the two frame members at the closed end of the film-receiving pocket, it is necessary to adopt various auxiliary measures, all of which involve disadvantages.
For instance, it is disclosed in Austrian Patent Specification No. 231,195 to bevel the side edges which define the above-mentioned film-receiving groove which is disposed opposite to the entrance slit. Said edges extend transversely to the direction in which the transparency is inserted. Owing to said beveled surfaces at said edges the transparency can easily slide from the entrance slit of the frame to the position for projection even if the transparency is not perfectly planar, and the groove will retain the film in the proper position.
The frames for use by amateurs usually have a thickness of 1.2 to 1.8 mm. In such frames the taper of the beveled surfaces at the edges of the picture gate is not sufficient for a safe insertion of a cambered film.
It is also known that the insertion of the transparency to the position for projection can be facilitated in that that edge of the frame which defines the rear edge of the picture gate is formed with a V-shaped recess. But such a recess can be provided in practice only in one half of the frame because the other half of the frame is required to define the projected picture. For this reason that feature can allow only for a camber in one direction. A film must usually be mounted in a frame with a predetermined orientation so that trouble due to cambered film can be avoided only in part by that known measure.
German Patent Specification No. 1,294,065 also deals with the difficulty that the film transparency may strike against the picture gate boundary at that end which is opposite to the entrance slit so that the transparency cannot be moved to its intended position. It is stated in German Patent Specification No. 1,294,065 that that disadvantage can be avoided in that each transparency is cut in the cutting station to have a concave edge at that end which will be the leading end as the transparency is inserted into a slide frame. But that measure requires an expensive cutting tool and will not be very effective because the concavity must be only small as the unexposed areas between the pictures on the film may be very narrow so that a strongly concave edge would be projected two.
From FIG. 15 of Published German Application No. 27 48 676 it is known to provide some clamping points near the rear end of the film-receiving pocket defined by the frame members so that the transparency will be frictionally retained at said clamping points against any desired displacement in the frame and will be held exactly in the desired position relative to the picture gate of the frame. Each of said clamping points is formed by a gently curved bulge, which is formed on one inside surface and protrudes into the film-receiving pocket, and a recess, which is formed in the opposite inside surface and registers with the bulge. By means of each bulge, the adjacent portion of the transparency will slightly be bent to enter the recess so that the transparency will be frictionally retained. That proposal has not proved satisfactory in practice because different films may differ in thickness. Besides, the constriction provided in the slotlike film track on the sides of the frame has rendered the insertion of the transparency more difficult because as the film is inserted it will strike against the bulges so that the film will be cambered and held back.
FIG. 8 of German Patent Specification No. 12 14 898 discloses a slide frame having two entrance slits, each of which opens directly, without a transition, into a filmreceiving pocket. Said frame comprises two frame members which have broadsides facing each other. The frame members are joined to each other at their corner portions and are unconnected between their corner portions disposed at corresponding ends of the two slits. When the corresponding corner portions of the frame are forced toward each other, the two frame members will gape between the corresponding corner portions and the frame will then assume a somewhat tubular shape. For this reason such slide frames can be described as having a tubular filmreceiving pocket. The tubular film-receiving pocket opens at each end into a slit. To ensure that the transparency will be retained in the frame although the film-receiving pocket is tubular, the frame is provided with limiting cams and grooves at the top and bottom of the pocket. The limiting cams and grooves are provided for guiding the transparency at its side edges. Additional means for guiding the transparency being inserted consist of bores, which receive pins of a mounting machine so that said pins constitute guide stops for the transparency.
The slide frame known from German Patent No. 1,214,898 can be expanded at one end or at the other end of its tubular film-receiving pocket. Such a slide frame having a tubular film-receiving pocket can be expanded more effectively and more easily at the expansible slits than a frame which has a blind film-receiving pocket that is open only at one end. A special advantage afforded by the tubular pocket resides in that a transparency can be inserted into the frame from one end or the other. This will be significant if the frame is used on an automatic mounting machine because in such machine a slide frame of that kind will no longer have to be pre-arranged to have a predetermined orientation, as will be necessary if a transparency is to be automatically inserted on such machine into a slide frame having a blind film-receiving pocket.